Zion National Park is only about 45 minutes outside of St. George, Utah. It's an easy drive, and St. George makes a good base camp for day trips into Zion. Any timeshare in St. George that suits you would be fine for that.
Las Vegas is only about two hours south of St. George, an easy drive down Interstate 15.
The Grand Canyon is a different matter. There is a North Rim and South Rim that many people visit. As far as I know, there are no timeshares convenient to the North Rim. But it is only a few hours from the East entrance to Zion National Park. So you technically "could" stay in St. George, and visit the North Rim, if you wanted to. Maybe do an overnight in a motel or the North Rim lodge inside the park, then head back to St. George the next day.
At the South Rim, you're not all that far from either Sedona or Flagstaff. Both cities have lots of timeshare choices. You could take your pick, and make trips to one of the South Rim entrances.
Driving to/from Las Vegas and the South Rim will be the longest part of that trip.
Others will certainly have other ideas, but this should help get you thinking about it. It's a great area to visit, and you'll be certain to enjoy yourself.
Have fun!
Dave
Has anyone traveled this triangle. Stayed at timeshares that made this workable. I would have access to II and RCI. Any opinions on this trip planned for late June or July of 2013. I know Las Vegas will be hot.
Thanks.
Gr